As depicted in FIG. 1, a typical shoulder or glenohumeral joint is formed in a human body where the humerus 10 movably contacts the scapula 12. The scapula 12 includes a glenoid fossa 14 that forms a socket against which the head 26 of the humerus 10 articulates. At this socket, the scapula 12 includes cartilage 16 that facilitates such articulation. Beneath the cartilage is subchondral bone 18 that forms a wall of a glenoid vault 20 that defines a cavity which contains cancellous bone 22. The subchondral bone 18 that forms the glenoid vault 20 defines a glenoid rim 24 at a periphery of the glenoid vault 20 that is attached to the cartilage 16. During the lifetime of a patient, the glenoid fossa 14 and/or the head 26 may become worn, especially at their posterior and/or superior portions thereby causing severe shoulder pain and limiting the range of motion of the patient's shoulder joint. To alleviate such pain and increase the patient's range of motion, a shoulder arthroplasty may be performed. Arthroplasty is the surgical replacement of one or more bone structures of a joint with one or more prostheses.
The goal of shoulder arthroplasty is to restore normal kinematics to the shoulder. Accordingly, known systems attempt to replicate the normal kinematics by carefully controlling the geometry of the articulating surfaces in the joint as well as the positioning of the prostheses in the bones in which the prostheses are implanted. Thus, the articulating surface of a humeral component is typically spherical, and positioning of the humeral component is accomplished by using the anatomical neck of the humerus as the reference plane for reconstruction of the humeral head.
In general, the head 26 of the humerus 10 may be resected using a saw or chisel and then planed flat. With the resected head 26 of the humerus 10 exposed, a drill guide pin may be used to insert a guide pin substantially through the center of the plane formed by resecting the head 26 of the humerus 10. The guide pin may then be used to guide subsequent instruments in the removal of bone from the humerus 10 in preparation for the insertion of a base portion of a humeral component. The guide pin may then be removed, and a base portion of a humeral component may then be inserted into the cavity. The final humeral head component size may then be determined by trialing one or more trial humeral head components on the base and performing a trial reduction of the joint. Once a trial reduction has been successfully performed, the trial head component may be removed, and the final head component may be mounted to the base.
While the foregoing procedure is generally effective, there are some drawbacks. As an initial matter, the guide pin is placed prior to positioning a trial head component on the humerus. Accordingly, the guide pin may not be optimally located. Additionally, a number of different instruments are required throughout the process. As the number of instruments increases, the cost and complexity of the procedure increases.
There remains a need for a shoulder arthroplasty system that provides for improved visualization of the head component position prior to implanting a base component. There is a further need for a shoulder arthroplasty system that facilitates positioning the base component. A shoulder arthroplasty system that reduces the number of instruments is also needed.